If Washington gives the Mexican president a pat on the back, it will be a stab in the back for the Mexican movement for justice and transparency.

Mexican President Enrique Peña Nieto is traveling to Washington, seeking to bolster his support in the United States as it rapidly unravels in his own country. But President Barack Obama has much to lose by propping up the faltering Mexican leader.

Protests over the murder of six people and the disappearance of 43 students from a rural teachers’ college in Ayotzinapa continue, both inside Mexico and among Latino communities in the United States. Demonstrations attended by hundreds of thousands of Mexicans began with the demand to bring the students back alive and have now broadened into a call for the president’s resignation.

The students were last seen being taken away by the local police of Iguala, Guerrero on the night of September 26. Three were killed when police opened fire on them without warning, and the rest were allegedly handed over to gang members. Protesters call the massacre a “crime of the state.”

The mayor of Iguala, José Luis Abarca, is being held for ordering the attacks and for colluding with the regional drug cartel, Guerreros Unidos. Feeling the heat, the state’s governor, Angel Aguirre Rivero, resigned on October 23. Civil society groups and a Twitter campaign are calling for an investigation of Aguirre for complicity in the crime and for protecting Abarca.

Nor are national authorities exempt. Recent evidence shows that the Mexican Army and Federal Police had knowledge of the incident before, during, and after it occurred. But although they were based just moments away, they did not protect the students. There is also evidence to suggest that they were directly involved in the crime.

Since the killings, the Peña Nieto administration has fumbled along in what appears to be a massive cover-up. The president first insisted that the crime was under the state government’s jurisdiction, despite the fact that transnational criminal organizations were implicated and that international law considers enforced disappearances “by their very nature a crime against humanity.

Later, Attorney General Jesus Murillo Karam announced a finding that the Guerreros Unidos gang had murdered the students and buried their bodies in clandestine graves. When the 30 bodies recovered turned out not to be the missing students, he declared that the criminals had incinerated the bodies at a dump in nearby Cocula and thrown the ashes in the river. One student was identified among remains found in bags in the river. But the parents and some forensics experts dispute the hypothesis of mass incineration at the dump.

We may never know the truth. Peña Nieto presides over a nation of impunity, where 98.3 percent of crimes go unpunished. The justice system has gotten worse, not better, under attempts at reform that have been heavily funded by the U.S. government.

Protesters today follow a long tradition of fighting for democracy in Mexico. After overthrowing a dictator in 1911, the country suffered years of bloodshed. Despite gains in social justice, authoritarian, one-party rule was established under the telling name of the Revolutionary Institutional Party (PRI, by its Spanish initials), whose rule lasted for 71 years.

Although the PRI achieved relative stability (a plus for trading partners like the United States), it instituted corruption and coercion as the modus operandi of politics. It was former PRI leader Carlos Hank González who coined the phrase “a poor politician is a bad politician” to reflect the assumption that part of a politician’s job is to syphon off public funds.

Peña Nieto’s election in 2012 marked the return of the PRI after the party lost the presidency in 2000 and again in 2006. Many, including a student movement called IAm132, warned of a return of the old ways.

Last year, journalists revealed that Peña Nieto’s family home was financed by a construction firm heavily favored with government contracts while Peña Nieto was governor of the state of Mexico, the populous federal state that borders Mexico City. This same firm was part of a consortium that was granted a contract for $3.7 billion to build a light rail line by Peña Nieto’s government. As a result of public outcry, the contract was rescinded. But questions about the $7-million mansion remain.

If Obama gives Peña Nieto the expected pat on the back, it will be a stab in the back to the Mexican movement for justice and transparency. Obama and Congress should instead announce their full support for a thorough investigation of the disappearances and the suspension of all police and military aid to Mexico. Congress must also immediately stop funding Plan Mexico — the drug war aid package formally known as the Merida Initiative that has appropriated about $2.4 billion to Mexico — and look closely and responsibly at what U.S. aid to Mexican security forces is actually supporting: namely, human rights abuses.

Our government should respect our own stated principles and laws on human rights and democracy, as well as Mexicans’ efforts to save their nation from the abyss into which it’s fallen.

President Obama must no longer lend U.S. political and economic support to an authoritarian system in crisis.